The invention relates to a steering wheel with an airbag module.
In steering wheels equipped with airbag modules, the airbag module is generally equipped on the driver side with a covering cap which is adapted visually and haptically to the installation environment, which cap at the same time forms the push-button region for actuation of the horn contact. This covering cap must be able to be easily torn open and swung open so that the gas bag arranged folded together therebeneath can emerge unimpeded and can unfold when it is inflated in an explosion-like manner as a function of a defined threshold deceleration of the vehicle. For these reasons, the covering cap must be constructed so as to be as low in mass as possible. It further follows from this that it can not be designed to be arbitrarily thick and rigid.
If, to actuate the horn contact, only the covering cap is to be arranged so as to be movable relative to the steering wheel, the problem arises that the covering cap can not be supported directly on the gas bag lying therebeneath, because otherwise the horn actuation would be hindered. On the other hand, with a covering cap only supported on the marginal side, the danger exists that the provided tearing and bending regions become weakened over time and partially break open, so that the gas bag space is no longer sealed to the exterior.
With regard to the above-mentioned difficulties, one therefore generally proceeds so that not only is the covering cap but the entire airbag module arranged movably relative to the steering wheel body so far that the horn contact can be actuated and released again. With such designs, usually there is one of the two contacts arranged fixed in position in the steering wheel body and the other contact fastened to the movable airbag module. In so doing, however, the difficulty arises that on installation of the airbag module in the steering wheel, one must take precise care to maintain the contact gap, because otherwise either no horn contact comes about or else the horn signal is triggered unintentionally by vehicle vibrations owing to too small a contact gap. The known design therefore not only requires a careful installation, but also the maintaining of close manufacturing tolerances in the production and assembly of all the components involved, which is time-consuming and costly.
The invention is based on the problem of constructing the horn contact for a steering wheel so that the manufacturing expenditure can be reduced without the reliability of operation being impaired. This is achieved in a steering wheel which comprises a steering wheel plane, an airbag module, a support plate and a spring plate connected to the support plate via an electrically insulating element. The steering wheel further comprises an insulating support fixed to the steering wheel, and restoring springs for replacing the airbag module in an initial position after displacement for actuation of a horn contact. The airbag module, for actuation of the horn contact, is constructed so as to be displaceable approximately perpendicularly to the steering wheel plane against the restoring springs by at least a contact gap. The airbag module is connected with the support plate extending substantially parallel to the steering wheel plane, the support plate being connected electrically to the vehicle, forming an earth contact and cooperating with the spring plate defining a counter-contact arranged so as to be electrically insulated with respect to the vehicle. The spring plate is aligned substantially parallel to the steering wheel plane and has at least one contact arm which is able to be deflected elastically approximately perpendicularly to the support plate and is able to be supported on a rear face on the insulating support.
The basic idea consists in arranging both contacts on the airbag module which is movably arranged with respect to the steering wheel and of providing in the steering wheel itself only an electrically insulating support, on which a contact arm, able to be deflected elastically, can rest on the rear face, so that in the case of pressure onto the covering cap and relative movement between airbag module and steering wheel it can be deflected and can be brought into electrically conducting connection with the support plate which is constructed as an earth contact.
In this way, a very precise installation gap can be maintained by simple means between the support plate and the contact arm. Except for the support arranged in the steering wheel, all the components which are involved are arranged on the airbag module, so that the installation contact gap is not impaired by the incorporation of the airbag module into the steering wheel. Care must merely be taken that the support, for the contact arm, on the steering wheel side is correctly positioned relative to the installation plane for the airbag module. Since, moreover, the play for the movement of the airbag module relative to the steering wheel body must always be distinctly greater than the gap for the horn contact, one can provide relatively large tolerances with respect to the arrangement of the support relative to the installation plane, because the contact arm does not compulsorily have to rest directly on the support as long as no actuation of the horn contact is desired. A certain xe2x80x9cidle strokexe2x80x9d up to the supporting of the contact arm on the support can be readily accepted, the relative movement between airbag module and steering wheel body being greater by the xe2x80x9cidle strokexe2x80x9d than the minimum contact gap which is to be maintained.